Server not starting. "Cannot invoke "aag.f()"
Solution 1:
I managed to find the Reddit thread, and it appears that the server could not start because the port was already in use.
Quit all other running Minecraft servers or change the port.
To change the port, open server.properties and replace port=oldport with port=newport.
When logging into the server change address to address:newport, or address:oldport to address:newport.